Complex RuHCl Research Articles

Ruthenium Complexes of a Triphosphorus-Coordinating Pincer Ligand: Ru–P Ligand-Substituent Exchange Reactions Driven by Large Variations of Bond Energies

The reaction of [(p-cymene)RuCl2]2 with the triphosphine ligand bis(2-di-tert-butylphosphinophenyl)phosphine (tBuPHPP) results in an unusual exchange reaction in which a chloride ligand and a phosphorus-bound H atom are exchanged ("H-P/Ru-Cl exchange") to give the (chlorophosphine)ruthenium hydride complex (tBuPClPP)RuHCl [1Cl-HCl; tBuPClPP = bis(2-di-tert-butylphosphinophenyl)chlorophosphine]. Density functional theory calculations indicate that the presumed initial product of metalation, (tBuPHPP)RuCl2 (1H-Cl2), undergoes an H-P/Ru-Cl exchange via sequential P-to-Ru α-H migration to give the intermediate (tBuPPP)RuHCl2, followed by Ru-to-P α-Cl migration to give the observed product 1Cl-HCl (crystallographically characterized). Dehydrochlorination of 1Cl-HCl under a H2 atmosphere gives (tBuPClPP)RuH4 (1Cl-H4), which then can undergo a second dehydrochlorination and addition of H2 to give (tBuPHPP)RuH4 (1H-H4). This reaction may proceed via the reverse of the intramolecular exchange by 1H-Cl2, i.e., loss of H2 from 1Cl-H4 to give 1Cl-H2, which could undergo Cl-P/Ru-H exchange to give (tBuPHPP)RuHCl (1H-HCl). Accordingly, the thermodynamics of Cl-P/Ru-H exchange are found to be highly dependent on the nature of the ancillary anionic ligand (H or Cl), which is not directly involved in the exchange. The origin of this thermodynamic dependence can be explained in terms of the high stability of complexes (RPXPP)RuHCl (X = H, Cl; R = Me, tBu), in which the hydride is approximately trans to a vacant coordination site and the central phosphine group is approximately trans to the weak-trans-influence chloride ligand. This conclusion has general implications for five-coordinate d6 complexes, both pincer- and nonpincer-ligated.

Unexpected CNN-to-CC Ligand Rearrangement in Pincer–Ruthenium Precatalysts Leads to a Base-Free Catalyst for Ester Hydrogenation

We report the conversion of a series of CNN–pincer–ruthenium complexes Ru(CNN)HCl(CO) to a CC-chelated form Ru(CC)(PR3)2H(CO) on reaction with sodium tert-butoxide and monodentate phosphines. When the phosphine is triphenylphosphine, cis-phosphine complexes form at room temperature, which convert to the trans isomer at elevated temperatures. When the phosphine is tricyclohexylphosphine, only the trans-phosphine isomer is observed. The CC-chelated complexes are active catalysts for the hydrogenation of esters, without the need for added base. The ligand structure–activity relationship in the series of CC-chelated complexes mirrors that in the precursor CNN-Ru complexes, potentially indicating a common catalytic mechanism. Density functional theory calculations establish a plausible mechanism for the CNN-to-CC rearrangement and demonstrate that this rearrangement is potentially reversible under the conditions of ester hydrogenation catalysis.

Synthesis of Unsymmetrical N-Heterocyclic Carbene–Nitrogen–Phosphine Chelated Ruthenium(II) Complexes and Their Reactivity in Acceptorless Dehydrogenative Coupling of Alcohols to Esters

Two novel ruthenium complexes RuH(CO)Cl(PPh3)(κ2-CP) (1) and [fac-RuH(CO)(PPh3)(κ3-CNP)]Cl (2) bearing unsymmetrical N-heterocyclic carbene–nitrogen–phosphine (CNP) were synthesized and characteriz...

Aperture-Opening Encapsulation of a Transition Metal Catalyst in a Metal–Organic Framework for CO2 Hydrogenation

The aperture-opening process resulting from dissociative linker exchange in zirconium-based metal-organic framework (MOF) UiO-66 was used to encapsulate the ruthenium complex (tBuPNP)Ru(CO)HCl in the framework (tBuPNP = 2,6-bis((di- tert-butyl-phosphino)methyl)pyridine). The resulting encapsulated complex, [Ru]@UiO-66, was a very active catalyst for the hydrogenation of CO2 to formate. Unlike the analogous homogeneous catalyst, [Ru]@UiO-66 could be recycled five times, showed no evidence for bimolecular catalyst decomposition, and was less prone to catalyst poisoning. These results demonstrated for the first time how the aperture-opening process in MOFs can be used to synthesize host-guest materials useful for chemical catalysis.

Dehydrogenative Coupling of Ethanol and Ester Hydrogenation Catalyzed by Pincer-Type YNP Complexes

The “Y” donor group (Y = −OMe, −SEt, −PPh2, −NH2, −NMe2, −Py, pyrrolidinyl, quinolyl) of the pincer-type ruthenium complexes RuHCl(CO)[κ3-YNP] has a dramatic influence on the catalytic activity in the dehydrogenative homocoupling and cross-coupling of ethanol and ester hydrogenation reactions. The observations are connected with the mechanisms of the catalytic reactions, and this paper provides evidence for ester C–O bond formation/cleavage assisted by the bifunctional catalysts in an outer-sphere fashion, reminiscent of the Tishchenko chemistry.

DFT Studies on the Reaction Mechanism of 1,3-Conjugated Dienes Isomerization Catalyzed by Ruthenium Hydride

The detailed reaction mechanism for the isomerization of 1,3-conjugated dienes catalyzed by the ruthenium hydride complex RuHCl(CO)(H2IMes)(PCy3) has been studied with the aid of density functional theory (DFT) calculations. Both cis and trans isomers of a 1,3-conjugated diene were considered as the reactants. For each isomer, two catalytic cycles were calculated, which (respectively) generate a 1,3-hydride shift product or a 1,5-hydride shift product. Both catalytic cycles proceed via alkene migratory insertion into the Ru–H bond, σ-allyl ruthenium isomerization, and β-H elimination steps. Our computational study shows that the cis isomer of the model reactant reacts preferentially via the pathway leading to the 1,5-hydride shift product, consistent with the experimental results. The σ-allyl ruthenium isomerization step is found to be crucial for reaction regioselectivity. Strong binding of the C═C bond to Ru is involved in the generation of the 1,5-hydride shift product. In addition, the steric effect o...

Ruthenium hydrides containing the superhindered polydentate polyphosphine ligand P(CH2CH2P(t)Bu2)3.

The complex RuH2(N2)(P(2)P3(tBu)) (1) containing the extremely bulky PP3-type ligand P(2)P3(tBu) = P(CH2CH2P(t)Bu2)3 was synthesized by reduction of RuCl2(P(2)P3(tBu)) (2) with Na/NH3 under a N2 atmosphere. Like other complexes containing the P(2)P3(tBu) ligand, only three of the four donor phosphines are coordinated, and one of the phosphines remains as a dangling pendant phosphine. Reduction of RuCl2(P(2)P3(tBu)) (2) with a range of the more usual hydride reducing agents afforded the previously unknown ruthenium hydride complexes RuHCl(P(2)P3(tBu)) (3), RuH(BH4)(P(2)P3(tBu)) (6), RuH(AlH4)(P(2)P3(tBu)) (7), and the ruthenium(II) trihydride K[Ru(H)3(P(2)P3(tBu))] (8). The ruthenium tetrahydride containing a coordinated H2 ligand RuH2(H2)(P(2)P3(tBu)) (10) was synthesized by exchange of N2 in 1 by H2. Complexes 1, 3, 6, 7, and 8 were characterized by crystallography and multinuclear NMR spectroscopy.

Catalytic Activity and Fluxional Behavior of Complexes Based on RuHCl(CO)(PPh3)3 and Xantphos-Type Ligands

With RuHCl(CO)(PPh3)3 as the starting material, the complexes RuHCl(CO)(PPh3)(L) were prepared for L = Xantphos and closely related ligands. Their catalytic activity in the direct amination of cyclohexanol showed large differences depending on the different backbone structures. In those complexes the Xantphos-type ligand backbones are slightly bent and display fluxionality, studied by VT-NMR. This was assigned to the “flipping” of the backbone via the bridging atoms in the xanthene backbone. Via line shape analysis of the peaks, the Gibbs free energy of activation of the flipping movement was found to be around 56 kJ/mol in all cases. However, the activation enthalpy and entropy differed considerably. Employing RuCl2(PPh3)3 as the precursor resulted in the trans-coordinated complexes RuCl2(PPh3)(L) for L = Xantphos, Sixantphos. Fluxionality was no longer observed, due to the fact that in these complexes the O atom in the backbone also coordinates to the Ru.

Stereoselective synthesis and luminescence properties of novel trans-regular N-alkylcarbazolylene–silylene–vinylene polymers

Novel trans-stereoregular silylene–carbazolylene–vinylene derivatives (13–15) were synthesized via silylative coupling reaction of 3,6-bis(dimethylvinylsilyl)-N-alkylcarbazole (7–9) catalyzed by ruthenium–hydride complex RuHCl(CO)(PCy3)2 (1). All products were isolated, fully characterized by spectroscopic methods and GPC analyses and their absorption and fluorescence properties were determined.

Monosubstituted Borane Ruthenium Complexes RuH2(η2:η2-H2BR)(PR′3)2: A General Approach to the Geminal Bis(σ-B–H) Coordination Mode

A series of borane bis(σ-B–H) ruthenium complexes RuH2(η2:η2-H2BR)(PR′3)2 (R = alkyl, aryl; R′ = Cy, Cyp, iPr) has been prepared by using two synthetic strategies. The first one is based on a simple substitution reaction by adding the corresponding monosubstituted H2BR borane to the bis(dihydrogen) ruthenium complex RuH2(η2-H2)2(PCy3)2. The second one, more general, results from the reaction of the chloro complex RuHCl(H2)(PR′3)2 (R′ = Cy, Cyp, iPr) with the corresponding lithium monosubstituted borohydrides RBH3Li (R = Mes, tBu, Me, C4H3S, Ph). All the complexes have been characterized by multinuclear NMR, IR, and X-ray diffraction studies. DFT calculations have been used to better define the bonding mode of the borane ligand to the metal center as well as to establish the thermodynamic cycle that delineates the coordination process. The tBu species displays a dynamic behavior evidencing an equilibrium between a borohydride and a σ-borane formulation. The thienyl case illustrates the competition between sulfur coordination and a bis(σ-B–H) coordination mode.

Ruthenium Carbene–Diether Ligand Complexes: Catalysts for Hydrogenation of Olefins

A series of carbene–diether ligands were prepared and the corresponding Ag salts used to prepare the complexes RuHCl(PPh3)2(Im(OR)2) (Im(OR)2 = C3H2(NCH2CH2OR)2; R = Me (4a), t-Bu (4b), tert-hexyl (4c), Ph (4d), 2,6-i-Pr2C6H3 (4e)). In an analogous fashion the species RuHCl(PPh3)2(Y2Im(OMe)2) (Y2Im(OMe)2 = Y2C3(NCH2CH2OMe)2; Y2 = C6H4 (4f), Y = Cl (4g), Me (4h)) were also synthesized. Similarly RuHCl(CO)(PPh3)2(Im(OMe)2) (5) was prepared and readily converted to RuHCl(CO)(SIMes)(Im(OMe)2) (6) via treatment with SIMes. The reaction of 4a with SIMes afforded RuHCl(SIMes)(Im(OMe)2)(PPh3) (7), which reacts subsequently with Na[BPh4] to give [RuH(Im(OMe)2)(SIMes)][(η6-Ph)BPh3] (8). In a series of tests, the species 4a–h, 5, 6, and 8 were shown to catalyze the hydrogenations of 1-hexene, cyclohexene, and dimethyl itaconate. From the activity of 4a–h it is clear that the capability of the carbene–ether substituents to coordinate to the metal as well as electron-donating substituents on the carbene fragment enhan...

Dimethylaminoborane (H2BNMe2) Coordination to Late Transition Metal Centers: Snapshots of the B–H Oxidative Addition Process.

The reaction of cyclodiborazane [Me(2)N-BH(2)](2) with the chloro(dihydrogen) ruthenium complex RuHCl(η(2)-H(2))(P(i)Pr(3))(2) (1) led to the formation of the unsymmetricaly coordinated dimethylaminoborane complex RuHCl(H(2)BNMe(2))(P(i)Pr(3))(2) (2). The dimethylaminoborane coordination (H(2)BNMe(2)) to the ruthenium center in 2 was carefully studied by combining X-ray, multinuclear NMR, and density functional theory (DFT) techniques, and compared with the recently reported osmium analogue which was originally formulated as a σ-B-H borinium complex [OsH(2)Cl(HBNMe(2))(P(i)Pr(3))(2)] (4). All our data are in favor of a bis(σ-B-H) coordination mode at a very activated stage in the case of the ruthenium complex 2, whereas in the osmium complex 4, full oxidative addition is favored leading to a complex better formulated as an osmium(IV) boryl species with an α-agostic B-H interaction. The synthesis and characterization of the symmetrical dihydride complex RuH(2)(H(2)BNMe(2))(P(i)Pr(3))(2) (3) from addition of the lithium dimethylaminoborohydride to 1 is reported for comparison.

Ruthenium-Catalyzed (2 + 2) Intramolecular Cycloaddition of Allenenes

We report a ruthenium-catalyzed (2 + 2) intramolecular cycloaddition of allenes and alkenes. We have found that the use of the ruthenium complex RuH(2)Cl(2)(P(i)Pr(3))(2), which has previously gone unnoticed in catalytic applications, is crucial for the observed reactivity. The reaction proceeds under mild conditions and is fully diastereoselective, providing a practical entry to a variety of bicyclo[3.2.0]heptane skeletons featuring cyclobutane rings.

Tridentate and Tetradentate Iminophosphorane-Based Ruthenium Complexes in Catalytic Transfer Hydrogenation of Ketones

Tetradentate iminophosphorane complexes [RuH(PNNP)][BArF4] (5) and [RuHCl(PNNP)] (6) (PNNP = PPh2CH2PPh2NCH2CH2NPPh2CH2PPh2), prepared by in situ deprotonation of the aminophosphonium ligands in the presence of the dihydrogen complex RuH(H2)(Cl)(PCy3)2, are active precatalysts for the catalytic transfer hydrogenation of ketones at 80 °C under basic conditions in HOiPr. Complex 6 was characterized by X-ray diffraction. With a predominant focus on acetophenone, a comparative study with [RuH(H2NNPP)(PCy3)][BArF4] (3) incorporating a tridentate ligand (H2NNPP = H2N(C6H4)NPPh2CH2PPh2) does not indicate an NH effect. It is postulated that the pentacoordinated configuration around Ru with a hydride trans to a vacant site is essential in the catalyst resting state; however, the stability of this structural arrangement is disadvantageous for high activities. Further mechanistic studies, including labeling experiments, indicate facile protonation of these systems and, in addition, structural variations as a function of protonating agent (HOiPr, HX, H2O). The hydrido(chloro) complex RuH(Cl)(HNP)(NP) (7) (NP = Ph2PCH2PPh2NCH2tBu) was also isolated and characterized by X-ray diffraction, and a hydrogen bond between the chlorine and the NH group of the pendant ligand was ascertained by DFT calculations.

Ruthenium Complexes Bearing N–H Acidic Pyrazole Ligands

AbstractChelate ligands containing at least one pyrazole group were treated with RuCl2(PPh3)3, RuHCl(CO)(PPh3)3 and RuH2(CO)(PPh3)3 to form ruthenium complexes bearing protic N–H groups in close proximity to the catalytically active ruthenium centre. In the case of the hydridoruthenium complex RuHCl(CO)(PPh3)3 the resulting complexes also contain abasic hydrido ligand. The combination of acidic and basic hydrogen species in one molecule and the arising two‐site reactivity was thoroughly investigated spectroscopically and by DFT calculations. Catalytic tests on the hydrogenation and transfer hydrogenation of acetophenone showed a general activity of these systems.

Ruthenium complexes of chiral diphosphinite ligands with cyclohexane orchiro-inositol backbones as catalysts for asymmetric hydrogenation reactions

Treatment of [RuCl2(COD)] n with the chiral diphosphinite ligand (1S,2S)-1,2-trans-bis-(O-diphenylphosphino)cyclohexane [(1S,2S)-14] and triethylamine gives the bis(diphosphinite) complex RuHCl[(1S,2S)-14]2 (15) in good yield. If (rac)-1,2-trans-bis-(O-diphenylphosphino)cyclohexane [(rac)-14] is used in place of (1S,2S)-14 in this reaction, a racemic mixture of RuHCl[(1S,2S)-14]2 and RuHCl[(1R,2R)-14]2 [(rac)-16] is formed. The X-ray crystal structure of (rac)-16·(2.5CH2Cl2) has been determined. Treatment of (rac)-16 with hydrogen in iso-propanol leads to the formation of a racemic mixture of RuH2[(1S,2S)-14]2 and RuH2[(1R,2R)-14]2 [(rac)-17]. The structure of (rac)-17 was confirmed by the X-ray analysis of a racemic crystal. Ruthenium mono(diphosphinite), diamine complexes of the general formula RuCl2(NN)(PP) are formed by the treatment of RuCl2(PPh3)3 with the appropriate diphosphinite (PP) and diamine (NN) ligands. In this way, the following complexes have been synthesized: RuCl2[(+)-DPEN][(1S,2S)-14] (18), RuCl2[(−)-DPEN][(1S,2S)-14] (19), RuCl2[(+)-DPEN][(1R,2R)-14] (20), RuCl2[(−)-DPEN][(1R,2R)-14] (21), RuCl2[(+)-DPEN][(rac)-14] (22), RuCl2[(−)-DPEN][(rac)-14] (23), RuCl2(D-NN2)[(1S,2S)-14] (24), RuCl2(EDA)[(1S,2S)-14] (25), RuCl2(D-NN2)(D-10) (26), RuCl2(EDA)(D-10) (27), RuCl2[(+)-DPEN](D-10Et) (28), RuCl2(D-NN2)(D-10Et) (29), [where DPEN = 1,2-diphenylethylenediamine, D-NN2 = 1D-1,2-dideoxy-1,2-diamino-3,4,5,6-tetra-O-benzyl-myo-inositol, EDA = 1,2-diaminoethane, D-10 = 1D-3,4-bis(O-diphenylphosphino)-1,2,5,6-tetra-O-methyl-chiro-inositol, D-10Et = 1D-3,4-bis(O-diphenylphosphino)-1,2,5,6-tetra-O-ethyl-chiro-inositol]. These ruthenium complexes catalyze the hydrogenation of the ketones acetophenone and 3-quinuclidinone to give the corresponding alcohols in high yields, but with moderate to low enantiomeric excesses.

Silyl and σ-silane ruthenium complexes: Chloride substituent effects on the catalysed silylation of ethylene

Silylation of ethylene by the chlorosilanes HSiMe(2)Cl and HSiMeCl(2) was catalysed by the bis(dihydrogen) complex RuH(2)(eta(2)-H(2))(2)(PCy(3))(2) (1). Dehydrogenative silylation leading to the formation of the corresponding vinylsilanes was in competition with hydrosilylation. The rate and selectivity of the reactions were influenced by the number of chloro substituents and the ethylene pressure. A comparative mechanistic study was performed in toluene-d(8) with the two chlorosilanes. Reaction of 1 with an excess of HSiMe(2)Cl (10 equiv.) produced the sigma-silane complexes RuH(2)(eta(2)-H(2))(eta(2)-HSiMe(2)Cl)(PCy(3))(2) (2Me(2)Cl), RuH(2)(eta(2)-HSiMe(2)Cl)(2)(PCy(3))(2) (3Me(2)Cl) and the silyl complex RuCl(SiMe(2)Cl)(eta(2)-H(2))(PCy(3))(2) (4Me(2)Cl), all characterised by multinuclear NMR spectroscopy. Complexes 2Me(2)Cl and 3Me(2)Cl adopt a cis configuration for the two bulky phosphine ligands as a result of stabilising SISHA (Secondary Interactions between Silicon and Hydrogen Atoms) interactions. Complex 4Me(2)Cl resulted from the stoichiometric reaction of HSiMe(2)Cl with 1 producing RuHCl(eta(2)-H(2))(PCy(3))(2)in situ which further reacted with evolution of H(2) and formation of 4Me(2)Cl. When reacting 1 with 10 equiv. of HSiMeCl(2), the corresponding complexes 3MeCl(2) and 4MeCl(2) were detected as well as traces of 2MeCl(2). The reactivity toward ethylene was then examined. Under catalytic conditions (excess silane in toluene-d(8), ethylene atmosphere) only two compounds could be characterised: free PCy(3) and the new (eta(6)-aryl)(disilyl) complexes of the general formula Ru(eta(6)-C(6)D(5)CD(3))(SiMe(3-n)Cl(n))(2)(PCy(3)) (6Me(3-n)Cl(n)-d(8), n = 1,2). The X-ray structure of 6MeCl(2) was obtained on a single-crystal at 160 K. When only 2 equiv. of HSiMe(2)Cl were added, the ethylene(silyl) complex RuH(SiMe(2)Cl)(C(2)H(4))(PCy(3))(2) (7Me(2)Cl) was obtained in addition to the organic products resulting from catalytic hydrogenation, hydrosilylation and dehydrogenative silylation, i.e. C(2)H(6) (major one), C(2)H(3)SiMe(2)Cl and C(2)H(5)SiMe(2)Cl. In the case of 2 equiv. of HSiMeCl(2), upon ethylene addition, 7MeCl(2) was formed in minority compared to a new disilyl complex Ru(SiMeCl(2))(2)(PCy(3))(2) (8MeCl(2)) characterised by NMR spectroscopy and X-ray diffraction on a single crystal at 160 K. In 8MeCl(2), a formal 14-electron species, stabilisation through two agostic C-H bonds of the cyclohexyl groups was ascertained by DFT calculations.

Synthesis of Monosubstituted Cyclopentadienyl Ruthenium Complexes from the Reactions of 6-Substituted Fulvenes with RuHCl(PPh3)3

Reactions between 6-substitued fulvenes and the hydride complex RuHCl(PPh3)3 are described. Treatment of RuHCl(PPh3)3 with fulvenes without sp3-CH protons at the carbon α to the exocyclic carbon of fulvene produces cleanly monosubstituted cyclopentadienyl ruthenium complexes (η5-C5H4R)RuCl(PPh3)2 via hydride transfer to the electrophilic exocyclic carbon of fulvenes. When fulvenes containing sp3-CH protons at the carbon α to the exocyclic carbon were used, the reactions produce the expected (η5-C5H4R)RuCl(PPh3)2 complexes along with minor amounts of vinylcyclopentadienyl ruthenium complexes due to dehydrogenation.

Aromatization of a Dihydro-3-ruthenaindolizine Complex

The complex RuHCl(η2-H2)(PiPr3)2 (1) reacts with KTp (Tp = hydridotris(pyrazolyl)borate) to give the hydride−dihydrogen derivative RuHTp(η2-H2)(PiPr3) (2), which has been characterized by X-ray diffraction analysis (dH−H = 1.00(3) Å). Treatment of a toluene solution of 2 with 2-vinylpyridine leads to the 1,2-dihydro-3-ruthenaindolizine derivative Ru(CH2CH2−C5H4N)Tp(PiPr3) (3). Complex 3 aromatizes in toluene at 80 °C to afford the 3-ruthenaindolizine complex Ru(CHCH−C5H4N)Tp(PiPr3) (4) by loss of a hydrogen molecule in the absence of any hydrogen acceptor. The aromatic character of 4 is supported by X-ray diffraction analysis, NMR spectroscopy, and DFT calculations.

Computational design of ruthenium hydride olefin-hydrogenation catalysts containing hemilabile ligands,

Three ruthenium hydridocarbonyl complexes containing bidentate hemilabile ligands have been evaluated as possible catalysts for the H2 hydrogenation of olefins. Our previous investigations of the mainstay hydridoruthenium catalyst, RuHCl(CO)(PR3)2 (1), indicated that the rate-limiting olefin-insertion barrier was increased by the need for an H2 molecule to act as a stabilizing two-electron donor. Using density functional theory (DFT) calculations, we have determined that a P,N phosphane-oxazoline would be suitable for stabilizing the metal center of the complex RuHCl(CO)(PiPr3)(DZ), where DZ is a neutral bidentate hemilable ligand. In the reaction catalyzed by this complex, the olefin insertion occurs before the coordination of H2, avoiding the entropic penalty of coordinating H2. We predict that the phosphane-oxazoline containing catalyst will have higher activity than 1 and a different rate-law, zero-order in [H2]. The oxazoline increases the strength of coordination of the ethylene due to stronger back-donation from destabilized Ru d-orbitals to the ethylene π* molecular orbital.